1976 Manfredonia accidental release of arsenic
In September 26, 1976, an industrial accident at an ANIC facility in Manfredonia, Italy, led to the release 39 tons of arsenic into the atmosphere. In addition to death animals and the hospitalization of several people immediately following the incident, environmental contamination in an area roughly 15 km2 surrounding the facility devastated local wildlife.
Source: Wikipedia — 1976 Manfredonia accidental release of arsenic (CC BY-SA 4.0)